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Tue, 31 Mar 2026 21:17:01 -0700 (PDT) From: Ethan Yang To: chenhuacai@kernel.org Cc: kernel@xen0n.name, loongarch@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org Subject: [PATCH v2] LoongArch: mm: fix FLATMEM ARCH_PFN_OFFSET for non-zero DRAM base Date: Wed, 1 Apr 2026 04:17:00 +0000 Message-ID: <20260401041700.3260-1-ethan.yang.kernel@gmail.com> X-Mailer: git-send-email @GIT_VERSION@ In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" With CONFIG_FLATMEM, pfn_to_page() is computed as: mem_map + (pfn - ARCH_PFN_OFFSET) LoongArch currently derives ARCH_PFN_OFFSET from PFN_UP(PHYS_OFFSET), while PHYS_OFFSET defaults to 0. On systems whose first DRAM range does not start at physical address 0, ARCH_PFN_OFFSET becomes smaller than the real RAM base PFN. As a result, pfn_to_page() points past the intended mem_map base during early memmap initialization. This causes struct page initialization to touch wrong entries and can lead to early boot failures in the memmap_init_range() path. Fix this by deriving ARCH_PFN_OFFSET from min_low_pfn, and initialize/ recalculate min_low_pfn from memblock_start_of_DRAM() in LoongArch memory init so PFN-to-page translation matches the actual DRAM base. This change only fixes the FLATMEM PFN base and does not alter the existing VA/PA linear mapping scheme. Signed-off-by: Ethan Yang --- v2: - Fixed tab-to-space formatting. --- arch/loongarch/include/asm/page.h | 3 ++- arch/loongarch/kernel/mem.c | 1 + arch/loongarch/kernel/setup.c | 1 + 3 files changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/loongarch/include/asm/page.h b/arch/loongarch/include/asm= /page.h index 327bf0bc9..80aea8b51 100644 --- a/arch/loongarch/include/asm/page.h +++ b/arch/loongarch/include/asm/page.h @@ -25,7 +25,8 @@ * used in our early mem init code for all memory models. * So always define it. */ -#define ARCH_PFN_OFFSET PFN_UP(PHYS_OFFSET) +extern unsigned long min_low_pfn; +#define ARCH_PFN_OFFSET min_low_pfn =20 extern void clear_page(void *page); extern void copy_page(void *to, void *from); diff --git a/arch/loongarch/kernel/mem.c b/arch/loongarch/kernel/mem.c index 8ab1ffedc..03835f8cb 100644 --- a/arch/loongarch/kernel/mem.c +++ b/arch/loongarch/kernel/mem.c @@ -46,6 +46,7 @@ void __init memblock_init(void) } } =20 + min_low_pfn =3D PFN_UP(memblock_start_of_DRAM()); max_pfn =3D PFN_DOWN(memblock_end_of_DRAM()); max_low_pfn =3D min(PFN_DOWN(HIGHMEM_START), max_pfn); memblock_set_current_limit(PFN_PHYS(max_low_pfn)); diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c index 839b23ede..625be2494 100644 --- a/arch/loongarch/kernel/setup.c +++ b/arch/loongarch/kernel/setup.c @@ -394,6 +394,7 @@ static void __init check_kernel_sections_mem(void) static void __init arch_mem_init(char **cmdline_p) { /* Recalculate max_low_pfn for "mem=3Dxxx" */ + min_low_pfn =3D PFN_UP(memblock_start_of_DRAM()); max_pfn =3D PFN_DOWN(memblock_end_of_DRAM()); max_low_pfn =3D min(PFN_DOWN(HIGHMEM_START), max_pfn); =20 --=20 2.47.3